From Wikipedia:
The River Sile is the Longest Karst Spring River in Europe.
The 95 km Sile is a resurgence river. Although modified radically down the centuries, the resurgence area still includes the typical natural elements such as springs ("fontanassi"), pools and marshland, bogs and a dense network of watercourses. As well as the vegetation typical of water-meadows and resurgence pools (Carex, Cirsium, Caltha palustris, Iris pseudacorus), there are also isolated trees and small woods, relicts of the previous coverage typical of the hygrophilous lowland forest facies consisting of poplar, willow, alder, oak, elm, maple etc.